This invention relates to time division multiple access communication systems.
Traditionally, user traffic in a code division multiple access system is circuit switched. Once a call has been set up, the connection is maintained throughout the duration of the service request. A dedicated traffic channel is assigned to each active user for both the uplink and the downlink. Each dedicated traffic channel is characterized by a unique spreading code. Throughout the entire session, the dedicated traffic channel is used exclusively by the active user.
The circuit switched method is robust, and result in high system capacity by supporting: macro-diversity (soft handover); power control; limited random access overhead.
However, in wideband multi-service code division multiple access systems, extremely burst traffic needs to be supported. Burst traffic is supported by adjusting the data rate, and hence the spreading factor and spreading code. However, the need to quickly adjust the spreading code leads to highly complex code allocation algorithms.
Another popular method for accommodating bursty services is through packet switched data. ETSI UMTS W-CDMA (European Telecommunications Standards Institute Universal Mobile Telecommunications Service Wide Band code Division Multiple Access) and ARIB W-CDMA (Association of Radio Industry Business Wide Band Code Division Multiple Access) propose to use RACH/FACH (Random Access Channel/Forward Access Channel) to transmit infrequent bursty packet data. The advantage of such a scheme is quick set up time. A dedicated traffic channel is not required.
However, this transmission mechanism uses open loop power control only, and macro-diversity is not supported.
Against this background, in accordance with the invention, there is provided a time division multiple access communication system, in which down link data are transmitted over a data channel in repeated time frames each containing a plurality of time slots, and down link set up information is transmitted over a control channel to indicate from which time slot a user terminal should extract data, each frame on the data channel including a user packet flag to indicate whether or not each time slot in the frame contains data, and each user terminal being responsive to the set up information and to the user packet flags to extract data from its assigned time slot in those frames which the slot is indicated to contain data.
A plurality of bursty packet data users may be multiplexed onto the same downlink dedicated traffic channel. The multiplexing scheme allows low complexity code allocation; macro-diversity and soft handover; low associated control overhead; and limited closed loop power control.